Metal-rubber adhesion system

ABSTRACT

Disclosed is an adhesive system for use in rubber stocks to increase the adhesion of the stock to metal. The invention finds its greatest utility in the production of vulcanized metalreinforced rubber articles such as hose, pneumatic tires and belts. The adhesive system of the invention comprises the following two elements: 1. A halogen-donating material such as an N,N-dihalosulfonamide or a cyclic N-haloamide (e.g. a halogenated hydantoin); and 2. A resorcinol type material such as resorcinol itself, maminophenol or a partially reacted resorcinol-formaldehyde resin.

United States Patent [191 Cantor Dec. 16, 1975 1 METAL-RUBBER ADHESION SYSTEM [75] Inventor: Stephen E. Cantor, Cheshire, Conn.

[73] Assignee: Uniroyal, Inc., New York, NY.

[22] Filed: June 11, 1974 [21] Appl. No.: 478,411

Related US. Application Data [62] Division of Ser. No. 319,273, Dec. 29, 1972, Pat. No.

[52] US. Cl. 156/124; 156/110 A; 156/333; 260/3; 260/844; 428/468 [51] Int. Cl. B2911 17/00; C09J 3/12; C08L 7/00 [58] Field of Search 156/110 R, 110 A, 110 MD, 156/124, 128 T, 333; 260/844, 845, 3;

[56] References Cited UNITED STATES PATENTS 2,581,920 /1952 Kuhn 156/333 2,720,479 /1955 Crawford et a1... 156/333 3,507,917 /l970 Peterson 260/543 A 3,517,722 /1970 Endter 156/334 3,728,192 /1973 Kindle et a1. 156/124 FOREIGN PATENTS OR APPLICATIONS 1,072,625 1960 Germany Primary ExaminerDouglas J. Drummond Assistant Examiner-John E. Kittle Attorney, Agent, or Firm-Bruce F. Jacobs, Esq.

[5 7 ABSTRACT 1. A halogen-donating material such as an N,N-dihalosulfonamide or a cyclic N-haloamide (e.g. a halogenated hydantoin); and

2. A resorcinol type material such as resorcinol itself, m-aminopheno'l or a partially reacted resorcinol-formaldehyde resin.

1 11 Claims, No Drawings METAL-RUBBER ADHESION SYSTEM This is a division of application Ser. No. 319.273, filed Dec. 29, 1972. now US. Pat. No. 3,862,883.

BACKGROUND OF THE INVENTION In the production of rubber articles such as hose, pneumatic tires or power transmission belts such as V-belts. toothed positive drive belts. etc.. it is generally necessary to reinforce the elastomer. In the past. textile materials have been employed for this purose. However, wire cord has been found to be more desirable under certain conditions of use, for example, in pneumatic tires of the radial ply type. Maximum reinforcement of the rubber is obtained when maximum adhesion is produced between the laminate of rubber and the reinforcing element to form a unitary structure. Of equal importance is the requirement that the laminate of the reinforcing element and rubber remain in a bonded relationship with each other throughout the useful life of the reinforced structure in which the laminate is used.

To achieve satisfactory rubber-to-metal bonding, numerous methods have been developed. For example US. Pat. No. 2,720,479 describes a system wherein a phenolic resin and a brominated isoolefin-polyolefin interpolymer are dissolved in a suitable liquid carrier and the resulting adhesive composition is spread on rubber which is to be bonded to metal. The rubber and metal are subsequently pressed together and vulcanized. US. Pat. No. 2,581,920 also describes the use of halogenated polymers to bond rubber to metal.

In US. Pat. No. 3,5l7,722 to Endter et al. a rubbermetal adhesion system is described which involves formation of a resorcinol-formaldehyde resin at the interface between the rubber and the metal, thereby bonding these members together. In forming the resin, compounds capable of liberating the methylene and resorcinol precursors of the resin are placed in the rubber stock. Upon vulcanization, the methylene and resorcinol are released and presumably react to form the resorcinol-fonnaldehyde resin.

SUMMARY OF THE INVENTION 'tion product of resorcinol and acetone (condensate of resorcinol and acetone in the ratio of one mole of resorcinol to about 0.5 to 2 moles of acetone).-or a condensation product of resorcinol and acetaldehyde (condensate of resorcinol and acetaldehyde in the ratio of one mole of resorcinol to about 0.5 to 1 mole of acetaldehyde). Such fusible partially reacted resorcinol-formaldehyde resins may be prepared in known manner by heating a concentrated aqueous solution of resorcinol and formaldehyde, with or without a catalyst such as oxalic acid. The ball and ring softening point (ASTM designation E28-58T) of such fusible partially reacted resins will generally be from about 60C. to l2()C. Such resorcinol-acetone condensates. which are white powders. may be prepared in known manner by reacting acetone and resorcinolindilute hydrochloric acid solution at temperatures from 35C. to 50C. for several hours. Such resorcinol-acetaldehyde condensates. which are tacky reddish oils. may be prepared in known manner by reacting acetaldehyde and resorcinol in dilute oxalic acid solution at C. for several hours.

- The halogen donors useful in the invention have been observed to fall into two classes. The first class comprises I N.N- dihalogenated aromatic sulfonamides wherein sulfonamide nitrogen is bonded to two atoms of chlorine bromine or iodine and the sulfonyl sulfur is bonded directly to the aromatic nucleus. Such sulfonamideshave the. general formula Y[SO NX 1,, where X is chlorine, bromine or iodine, Y is phenyl, naphthyl,

biphenyl or biphenyl or can be unsubstituted or can be substituted with alkyl (especially lower, i.e. C, to C alkyl) or aryl (especially phenyl) moieties. a

Representative sulfonamide halogen donors used in the practice of this invention include those having the following structural formulae:

so it and where X is either chlorine, bromine or iodine, A may be zero (i.e. the aryl groups may be linked by a single covalent bond as where the biaryl group is biphenyl), oxygen(oxy), sulfur(thio), C to C alkyle'ne or alkylidene, and R represents hydrogen, alkyl (especially C to Cg lower alkyl) or aryl (especially phenyl) moieties. The sulfonamide halogen donors employed in the present invention are best prepared as described in copending U.S. Patent Application Ser. No. 207,647, filed Dec. 13, 1971 by Stephen E. Cantor, now US. Pat. No. 3,808,176 by reacting the corresponding unhalogenated aryl sulfonamides with an alkali metal hypohalite.

A second class of halogen donors employed in the invention comprises saturated, heterocyclic amides having a carbonyl carbon situated in the ring, with the carbonyl carbon being bonded to two N-halogenated nitrogen atoms both of which also reside in the hetero- -cyclic ring, i.e. the heterocyclic ring systemis characterized by the grouping:

XOX

wherein X is a halogen such as chlorine, bromine or iodine. The cyclic amides may be further exemplified by hydantoins corresponding to the structural formula:

wherein X is chlorine, bromine or iodine and R and R are hydrogen or alkyl groups having from 1 to 4 carbon atoms, with the total of the carbons in both groups not exceeding 8. Other examples of suitable cyclic amides include: tetrachloroglycoluril and trichloroisocyanuric acid The method of preparation of the cyclic amides is well known. See for example l-lenze et al. in J.A.C.S., Volume 64, pages 522-23 (1942), wherein hydantoins are formed by reacting the corresponding carbonyl compound with potassium cyanide and ammonium carbonate. In US. Pat. 2,920,997, Wolf et al. describe preparation of halogenated hydantoins by reacting a hydantoin precursor with chlorine or bromine. Halogenated isocyanurioacid may be prepared by introducing halogen into a suspension'of cyanuric acid as described in German Pat. No. 1,072,625. Similarly, the halogenated'glycoluril is prepared by reacting a halogen with the corresponding non-halogenated glycoluril. Other useful methods of synthesizing the cyclic amides are set forth in Beilstein Volume 1. XXVI H 441, E l 131 and E ll 260 and in Beilstein Volume ll H 598.

In practice of the invention, the halogen donor and resorcinol-type compound are mixed in a Banbury or other suitable mixer with a vulcanizable rubber elastomer and other conventional ingredients such as carbon black, rubber processing or softening oils which may be added as such or may be present from oil-extended rubbers, antioxidants, sulfur, zinc oxide and accelerators. This rubber composition is then coated (as by calendering) onto a metallic reinforcing element (e.g. metallic tire cord material). Subsequently, the reinforced rubber assembly is built into the desired article (e.g. a pneumatic tire) and vulcanized.

The amounts of halogen donor and resorcinol compound employed are not critical. The amount of resorcinolcor npound employed is generally from 0.5 to 5 parts per 100 parts of dry rubber and preferably is from 1 to.3 parts. The ratio by'weight of halogen donor to resorcinol compound will often be from 1 to 2. The total amount of the donor and resorcinol compound mixed with the rubber will often be from 0.1 to 10 parts per hundred of the rubber hydrocarbon.

Rubber elastomers employed in the invention are any of the highly unsaturated elastomers (by which is meant rubbery polymers of aliphatic conjugated diolefins and copolymers of such diolefins and one or more other unsaturated monomers, which copolymers contain copolymerized therein at least 25% by weight of aliphatic cconjugated diolefin) typified by natural rubber (NR), butadiene -styrene rubber copolymers (SBR), butadiene-acrylonitrile rubbery copolymers (NBR), so-called synthetic natural rubber, i.e. synthetic polyis oprene high in cis-l,4 configuration (IR), rubbery polybutadienes (BR), etc.

The following examples illustrate the invention. The wire tire cord used in the examples was of a 5 70.0058 inches over twisted 3 l l construction commonly employed in making the plies of a pneumatic tire. The surface of each strand of steel wire was coated with brass (an alloy of copper and 30% gram of steel i 1.5 grams.

The unaged or "green" adhesion of the rubber compounds was measured at 72F. after the cable was coated with the rubber compound being tested and the assembly vulcanized at 320F. for 30 minutes. The pounds necessary to pull the adhered cable free from the rubber is the adhesion value in pounds. The aged adhesion of the compounds was determined at 250F. after the rubber-cable assembly has been vulcanized at 320F. for 30 minutes. The adhesion tests were conducted following ASTM test number D-2229-68. Unless otherwise indicated, all parts and percentages referred to herein are by weight.

EXAMPLE l acid. parts of naphthenic oil and 1 part of an antioxi- 7 dant, namely a reaction product of diphenylamine and diisobutylene (Octamine Trademark of Uniroyal. lnc.) To this masterbatch was added 0.5 parts of N-tbutyl-Zbenzothiazole sulfenamide, (Delac NS Trademark of Uniroyal, lnc.), 0.5 parts of tetramethyh thiuram disulfide (Tuex Trademark of Uniroyal, Inc.) and 1 part of sulphur.

ln runs A through F, a condensation product of 1.0 part of resorcinol with 1.0 part of acetaldehyde was added as the resorcinol compound. The amount of this condensation product used was 2 parts per 100 parts of rubber. Additionally. 1 part of each of various halogen donors per 100 parts of rubber were incorporated as indicated in Table I.

A control rubber compound was prepared in a manner similar to that described above except that the resorcinol-type compound and halogen donor were omitted. This was used in Control l.

Adhesion results obtained are shown in Table I.

Sulfonam idc From Table I, it can be seen that the stock of Control 1 showed an unaged adhesion of pounds per inch with stock adhering to 25% of the wire after the wire had been withdrawn from the sample. This indicates that in the green or unaged state, the wire to rubber bond was relatively weak. After aging (as described above the adhesion was reduced to approximately 63 pounds per inch. However. the'amount of stock adhering to the wire had fallen to almost nothing. This indicates that the green adhesion was further weakened by aging.

By comparison, it will be ,noted from Table I that green adhesion in runs A through F always exceeded 1 10 pounds per inch as opposed to 85 pounds for the control. lndeed trichloroisocyanuric acid and N.N-dichloro-p-toluene sulfonamide exhibited green adhesions of approximately and 159 pounds respectively which are more than l.7 times the green adhesion exhibited by the control.

Upon aging. the adhesion in runs A through F remained relativelyconstant, i.e. it increased somewhat in runsB; C', D and E and decreased slightly in runs A and F. This constrasts markedly with Control 1 where. upon aging, a marked decrease in adhesion was noted. Even in runs A and C, which exhibited the lowest aged adhesion (approximately 1115 pounds), the aged adhesion was almost twice the aged adhesion of Control 1 (63 pou'nds). i V

It should alsobe noted that even after aging," runs A through F showed good coverage of the wire with stock after the'wire had been withdrawn. This should be contrasted with almost no'stock remaining in Control 1 after aging further illustrates that aging does not significantly harm adhesion obtained by the present invention. 7

EXAMPLE 2 This example is presented to illustrate the improved adhesion of the invention (run G) as contrasted with Control 2 which employed a halogen donor but did not employ the resorcinol-donating component of the invention.

The ingredients employed, and aging and testing of the stocks were as described in Example 1. In both run G and in Control 2, the halogen donating material was the benzene sulfonamide l phr) corresponding to the structural formula:

In run G, the resorcinol donor was the same material as was used in Example 1 (2 phr).

The adhesion levels (both green and aged) for run G and Control 2 are set forth in Table II.

From Table ll it will be seen that the green adhesion achieved in run G Wasapproximately 30% better than the green adhesion level of Control 2 (160 pounds vs. .1 18 pounds). Also in run G, the very high portion of rubber covering the wire in the green example demon- .strates that a very strong metal-rubber bond was obtained. Upon aging, the adhesion levels in both run G and in Control 2 remained relatively constant with the adhesion in run G remaining superior to Control 2.

While the mechanism of the present inventionv is not fully understood, one can speculate that the halogen donor provides labile halogen in the free radical form which may attack the metal surface of the wire and thereby contribute to adhesion as seenin Control 2. However, this does not explain the increase in adhesion levels obtained when the resorcinol-donating component of the invention was employed in combination with the halogen donor. To illustratethe efficacy of the halogen donor alone, it will be noted that the adhesion levels of Control 2 compare favorably with runs A through D (which exemplify the invention) and which are set forth in Table I. However, even the fairly good adhesion levelsobtained in Control 2 are markedly improved when the halogen donorof Control 2 is employed in combination with a resorcinol donor as illustrated in run G typifying the invention.

EXAMPLE 3 This exampleis presented to illustrate the effect on adhesion of the resorcinol donor alone. The run is denoted as Control 3. This should be contrasted with Control 1, where neither the resorcinol nor halogen donor was employed, and also with Control 2 where only a halogen donor was employed.

In Control 3, the type of ingredients, aging and testing of the stocks resembled Example 1. The resorcinol donor employed was the same compound as was used in Example 1 (2'phr).

For the green stock of Control 3, the pull required to extract the wire from the stock was about 87 pounds per inch with the extracted wire being covered with rubber. Upon aging as described in Example 1, the adhesion level was about 79 pounds per inch while the wire coverage was about 80%.

By comparison of Control 3'with Control 1, it can be seen that the poor adhesion level in Control 1, as measured in pounds of pull required to extract the wire, was not appreciably improved by incorporation of the resorcinol donor alone in the stock. The adhesion levels of Control 3 were also markedly inferior to those of the invention; see runs A through D.

In Control 3, the green wire coverage was about 80% which compares favorably with runs A through F exemplifying the invention. However, this relatively high wire coverage could easily be due to weakness in the stock rather than a superior rubbermetal bond. Upon aging, the wire pull test revealed that the adhesion level in Control 3 was very little improved over Control 1, i.e. use of the resorcinol donor did not appreciably increase the adhesion.

From Control 3, it can beseen that use of a resorcinol donor alone results in'little, if any, improvement in metal-rubber adhesion. From Control 2, (Example 2) it can be seen that use of a halogen donor alone may result in improving adhesion. Surprisingly, it has been discovered that when the relatively inactive resorcinol donor is employed in combination with a halogen donor, the resultingrubber-to-metal adhesion is far superior to that obtained by use of either the resorcinol compound or the halogen donor alone.

In the interest of technical completeness, TABLE III sets forth the dataon the physical properties of which were measured for both the uncured stocks and the vulcanizates made in accordance with all of the runs of Example 1, Run G of Example 2 and Control 3 of Example 3. It will be seenthat all of the stocks reported in TABLE [II had nearly identical uncured properties and were cured to essentially the same physical properties; while the incorporation of the N-halo compounds tended to show the rate of cure and to produce vulcanizates with lower tensile strength, the values obtained for physical properties are more than sufficient to fabricate finished articles.

TABLE lll Physical Properties of Stocks Containing Various N-Halo Compounds Control 1 Control A B C D F G 3 ML-4 at 212F. 46

Cure Rate 3 Mooney Search at 270F.

TABLE [ll-continued Physical Properties of Stocks Containing Various NHalo Compounds Control Control l A B C D E F G 3 Cured at 320F. for 30 min.

5-300 l76U I330 lSUU I570 I360 I550 l590 I400 I820 Tensile 3251) 2600 2680 2640 2340 2820 2 l 80 3010 I400 Elongation 520 5 l() 430 470 460 460 400 5 l (l 380 While the invention is of particular value for enhancing the adhesion of rubber to brass-coated or bronzecoated steel wire, and while the foregoing specific examples exemplify the invention as applied to brasscoated steel wire, it will be understood by those skilled in the art that the invention can be used for enhancing the adhesion of rubber to reinforcing elements having metal surfaces broadly. Thus, it is applicable, for example. with glass fiber coated with metals and alloys of metals including lead, zinc, tin, copper, aluminum, silver, etc. In other words, it can be used to promote the adhesion of rubber to any metal to which rubber can be made to adhere when vulcanized in contact therewith.

I claim:

1. In the method of adhering a metallic reinforcing element having a surface of brass to rubber by applying a vulcanizable rubber composition to the element and heating the assembly to vulcanize the rubber, the steps comprising:

Incorporating in the rubber composition before vulcanization a halogen donor selected from the group consisting of l) N,N-dihalogenated aromatic sulfonamides wherein the sulfonamide nitrogen is bonded to two atoms of chlorine, bromine or iodine and the sulfonyl sulfur is bonded directly to the aromatic nucleus and 2) cyclic N-halogenated amides wherein a carbonyl carbon in the ring is bonded to two nitrogen atoms, each of said nitrogen atoms in turn being bonded to a halogen atom thereby forming the grouping wherein X is chlorine, bromine or iodine and,

B. Incorporating in the rubber composition a member selected from the group consisting of resorcinol, m-aminophenol, m-phenylene diamine, resorcinol monoacetate, resorcinol diacetate, l,5-naphthalenediol, partially reacted resorcinol-formaldehyde resins, condensation products of resorcinol and acetone, and condensation products of resorcinol and acetaldehyde.

2. A method as in claim 1 wherein the halogen donor is an N,N-dihalogenated aromatic sulfonamide as defined in Claim 1 and having the general formula Y(- SO NX where X is chlorine, bromine or iodine, Y is phenyl, naphthyl, biphenyl or where Z is oxygen, sulfur, or alkylene or alkylidene having from 1 to 3 carbon atoms, and n has a value of 2 or 3.

3. A method vas in claim 2 wherein the members of the Y group are substituted with a lower alkyl having from 1 to 8 carbon atoms or with a phenyl group.

4. A methodasjn claim 1 wherein the halogen donor is N,N-dichlorobenzene sulfonamide.

5. A method as in claim 1 wherein the halogen donor is N.N,N',N tetrachloro-oxy-bis (benzene sulfonamide).

6. A method as in claim 1 wherein the halogen donor is N,N-dichloro-p-toluene sulfonamide.

7. A method as in claim 1 wherein the halogen donor is a hydantoin having the general formula:

donor is trichloroisocyanuric acid. 

1. IN THE METHOD OF ADHERING A METALLIC REINFORCING ELEMENT HAVING A SURFACE OF BRASS TO RUBBER BY APPLYING A VULCANIZABLE RUBBER COMPOSITION TO THE ELEMENT AND HEATING THE ASSEMBLY TO VULCANIZE THE RUBBER, THE STEPS COMPRISING: INCORPORATING IN THE RUBBER COMPOSITION BEFORE VULCANIZATION A HALOGEN DONOR SELECTED FROM THE GROUP CNSISTING OF 1) N,N-DIHALOGENATED AROMATIC SULFONAMIDES WHEREIN THE SULFONAMIDE NITROGEN IS BONDED TO TWO ATOMS OF CHLORINE, BROMINE OR IODINE AND THE SULFONYL SULFUR IS BONDED DIRECTLY TO THE AROMATIC NUCLEUS AND 2) CYCLIC NHALOGENATED AMIDES WHEREIN A CARBONYL CARBON IN THE RING IS BONDED TO TWO NITROGEN ATOMS, EACH OF SAID NITROGEN ATOMS IN TURN BEING BONDED TO A HALOGEN ATOM THEREBY FORMING THE GROUPING
 2. A method as in claim 1 wherein the halogen donor is an N,N-dihalogenated aromatic sulfonamide as defined in Claim 1 and having the general formula Y(SO2NX2)n where X is chlorine, bromine or iodine, Y is phenyl, naphthyl, biphenyl or
 3. A method as in claim 2 wherein the members of the Y group are substituted with a lower alkyl having from 1 to 8 carbon atoms or with a phenyl group.
 4. A method as in claim 1 wherein the halogen donor is N,N-dichlorobenzene sulfonamide.
 5. A method as in claim 1 wherein the halogen donor is N,N,N'', N''-tetrachloro-oxy-bis (benzene sulfonamide).
 6. A method as in claim 1 wherein the halogen donor is N,N-dichloro-p-toluene sulfonamide.
 7. A method as in claim 1 wherein the halogen donor is a hydantoin having the general formula:
 8. A method as in claim 1 wherein the halogen donor is 1,3-dichloro-5,5-dimethylhydantoin.
 9. A method as in claim 1 wherein the halogen donor is 1,3-dibromo-5,5-dimethylhydantoin.
 10. A method as in claim 1 wherein the halogen donor is tetrachloroglycoluril.
 11. A method as in claim 1 wherein the halogen donor is trichloroisocyanuric acid. 